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Bureau of Mines Information Circular/1984 




Retrofit Noise Control Modifications 
for Crushing and Screening Equipment 
in the Nonmetallic Mining Industry, 
An Applications Manual 

By R. J. Pokora, T. G. Bobick, and T. L. Muldoon 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 8975 

Retrofit Noise Control Modifications 
for Crushing and Screening Equipment 
in the Nonmetallic Mining Industry, 
An Applications Manual 

By R. J. Polcora, T. G. Bobicic, and T. L. Muldoon 




UNITED STATES DEPARTMENT OF THE INTERIOR 
William P. Clark, Secretary 

BUREAU OF MINES 
Robert C. Norton, Director 






\ 



fiH' 



Library of Congress Cataloging in Publication Data: 



Retrofit noise control modifications for crushing and screening equip- 
ment in the nonmetallic mining industry. 

(Information circular / United States Department of the Interior, 
Bureau of Mines ; 8975) 

Supt. of Docs, no.: I 28.27:8975. 

1. Sand and gravel plants— Noise control. 2. Crushed stone in- 
dustry—Noise control. 3. Crushing machinery —Noise. 4. Screens 
(Mining)— Noise. I. Pokora, R. J. (Robert J.). II, Series: Information 
circular (United States. Bureau of Mines) ; 8975. 



TN295.U4 [TD893.1V15] 622s [622'. 73] 84-600017 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Federal noise regulations 2 

Background 2 

Noise source Identification 3 

Noise control treatments 4 

Noise control treatment costs 4 

Manual organization and content 4 

Noise control treatment of the screen feed chute 5 

Design and selection of resilient Impact pads 6 

Installation of the chute wall Impact pad 7 

Installation of an Impact pad or dead bed In the chute bottom 8 

Noise control treatment of screens 9 

Design and selection of noise control treatments for screens 9 

Installation of noise control treatments for screens 11 

Noise control treatments for a cone crusher 17 

Design and selection of noise control treatments for cone crushers 17 

Installation of noise control treatments for crushers 18 

Noise control using an operator control booth 21 

General selection guidelines 21 

General construction guidelines 22 

Typical booth Installation 22 

Summary and conclus Ions 24 

ILLUSTRATIONS 

1. Product feed path from the belt conveyor to the screen feedbox 5 

2. Effect of Impact angle of product on resilient pad life 6 

3. Use of a profiled Impact pad to provide a better Impact angle for In- 
creased wear life 6 

4. Installation of a prof lled-surf ace Impact pad 7 

5. Installation of a resilient Impact pad may cause a change In product 
rebound 7 

6. Installation of a resilient Impact pad on the bottom of the screen feed 
chute 8 

7. Impact pad fastened to the bottom of feed chute with countersunk holes for 
protection of boltheads 8 

8. Installation of a dam to create a dead bed on the chute bottom 9 

9. Combination of a resilient Impact pad and dead bed In the bottom of a 

secondary screen feed chute 9 

*^ 10. Cross section of typical resilient protection for sizing screens 11 

\. 11. Installation of a bolted resilient screen deck and blank Impact panel 12 

^n 12. Bolted resilient deck with blank panel in the feedbox 12 

13. Resilient feedbox with impact pad where product from the chute strikes the 

f eedbox 12 

"^ 14. Installation of resilient side wing liners 13 

^, 15. Resilient liners bolted to screen side wings 13 

.sA 16. Installation of a resilient screen deck using side-tension rails 13 

^^ 17. Resilient screen deck with resiliently lined, side-tension rails 13 

^ 18. Resilient deck Installed on a horizontal screen using resiliently lined, 

side-tension rails and J-hook clamps 14 



ii 



ILLUSTRATIONS— Continued 

Page 

19. Treatment of the screen discharge lip 14 

20. Resilient discharge lip with thicker side liners to funnel the screen 

discharge 14 

21. Installation of resilient liners on a screen discharge chute 15 

22. Resilient liner in a screen discharge chute directly feeding a crusher.... 15 

23. Installation of a drag curtain over the feed chute discharge 16 

24. Drag curtain installed on an inclined screen 16 

25. Resilient liner installed in the crusher feed hopper 18 

26. Installation of a resilient crusher feed cone shell liner 19 

27. Installation of a one-piece resilient crusher feed cone liner 19 

28. Installation of resilient feed cone liner segments 20 

29. Installation of a resilient crusher feed plate 20 

30. Installation of a molded resilient pad for the mantle hold-down cap 20 

31. Installation of a barrier curtain around the crusher main frame 21 

32. Noise barrier curtain installed around the crusher main frame 21 

33 . Basic control booth wall construction 22 

34. View of a primary crushing plant with an operator control booth 23 

35. Operator control booth mounted on separate steel support structure 23 

36. Separate control booth support structure constructed by quarry personnel.. 23 

37. Primary crusher operator at the control station inside the booth 23 

TABLE 

1 . Permissible noise exposures 2 





UNIT 


OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


dB 




decibel in inch 


dBA 




decibel, A-weighted pet percent 


ft 




foot ton/h ton per hour 


h 




hour 



RETROFIT NOISE CONTROL MODIFICATIONS FOR CRUSHING AND SCREENING 

EQUIPMENT IN THE NONMETALLIC MINING INDUSTRY, 

AN APPLICATIONS MANUAL 

By R, J, Pokora, ^ T. G. Bobick, ^ and T, L, Muldoon^ 



ABSTRACT 

This Bureau of Mines report is an applications manual that can be used 
by the nonmetallic mining industry for guidance in installing noise con- 
trol materials into crushing and screening plants. These noise control 
modifications were installed and successfully tested at three operating 
quarries. This report identifies the major noise sources that can be 
encountered in crushing and screening plants, and discusses the applica- 
ble noise control materials and techniques that a plant operator can 
utilize on a retrofit basis to reduce equipment noise. 



^Program manager, CARD, Inc., Niles, IL (formerly with Foster-Miller Associates) 
fining engineer, Pittsburgh Research Center, Bureau of Mines, Pittsburgh PA. 
■^Senior engineer, Foster-Miller Associates, Inc., Waltham, MA. 



INTRODUCTION 



FEDERAL NOISE REGULATIONS 

Noise levels generated by the crushing 
and screening of nonmetallic minerals are 
regulated under 30 CFR, Part 56 — Safety 
and Health Standards — Sand, Gravel, and 
Crushed Stone Operations. Section 56.5- 
50 states: 

Mandatory. (a) No employee shall 
be permitted an exposure to noise in 
excess of that specified in table 1. 

TABLE 1. - Permissible noise exposures 



Duration per day, 
hours of exposure 



Sound level, dBA, 
slow response 



8 90 

6 92 

4 95 

3 97 

2 100 

1-1/2 102 

1 105 

1/2 110 

1/4 or less 115 

NOTE. — No exposure shall exceed 115 
dBA. Impact or impulsive noises shall 
not exceed 140 dB, peak sound pressure 
level. 

NOTE: When the daily noise expo- 
sure is composed of two or more peri- 
ods of noise exposure at different 
levels, their combined effect shall 
be considered rather than the indi- 
vidual effect of each. 



If the sum 



(Ci/T,) + (C2/T2) + . 



(Cn/Tn) 



exceeds unity, then the mixed expo- 
sure shall be considered to exceed 
the permissible exposure, Cn indi- 
cates the total time of exposure at 
a specified noise level, and Tp in- 
dicates the total time of exposure 



permitted at that level. Interpola- 
tion between tabulated values may be 
determined by the following formula: 

Log T = 6.322 - 0.0602 SL, 

where T is the time in hours and SL 
is the sound level in dBA. 

(b) When employees' exposure ex- 
ceeds that listed in table 1, feasi- 
ble administrative or engineering 
controls shall be utilized. If such 
controls fail to reduce exposure to 
within permissible levels, personal 
protection equipment shall be provid- 
ed and used to reduce sound levels to 
within the levels of the table. 

Enforcement of the standards has shown 
that an acute noise exposure problem ex- 
ists in the sand and gravel and crushed 
stone industries. 

BACKGROUND 

In 1981, a Bureau of Mines study'* of 
the noise exposures of workers in crush- 
ing and screening plants concluded that 
plant operators and plant cleanup person- 
nel can have full-shift noise exposures 
that range from three to four times that 
allowed by the standard. The study also 
included an analysis of the major noise 
sources that contribute to the overexpo- 
sure problem. 

As part of this same research program, 
retrofit noise control treatments for 
the major sources were designed, in- 
stalled, and evaluated in three crushing 
and screening plants. The three plants, 

4pokora, R. J., and T. L. Muldoon. 
Demonstration of Noise Control Techniques 
for the Crushing and Screening of Non- 
metallic Minerals (contract J01 00038, 
Foster-Miller, Inc.). BuMines OFR 50-83, 
1981, 187 pp.; NTIS PB 83-173039. 



which were selected from a series of 
eight surveyed, included — 

• A primary crushing plant that re- 
ceived run-of-mine product from the quar- 
ry. The plant used a 16-ft by 42-in vi- 
brating feeder grizzly and a 32- by 42-in 
jaw crusher. 

• A secondary plant that used a 5- by 
14-ft inclined double-deck screen, and a 
4-1/4-ft cone crusher. 

• A secondary plant that used a 5- by 
14-ft horizontal double-deck screen, and 
a 5-ft cone crusher. 

All three plants had a capacity of 200 to 
300 ton/h. 

The noise control treatments described 
in this manual were developed for this 
program and are, therefore, somewhat spe- 
cific to these sizes and types of plants. 
The basic treatments, however, with some 
modifications, are applicable to all 
crushing and screening plants, 

NOISE SOURCE IDENTIFICATION 

The first step in any noise control 
effort is to determine what noise sources 
are contributing most significantly to 
the overexposure problem. Noise level 
measurements, coupled with on-site obser- 
vations, identified the following major 
noise sources as those that could be 
treated in the field: 

Screen feed ehute, — Typically, mate- 
rial enters the screen through a steel 
chute from a belt conveyor. The product 
discharged from the conveyor impacts the 
sides, wall, and bottom of the steel 
chute. 

Screen feedhox. — Additionally, the 
product discharging from the screen feed 
chute impacts a steel screen feedbox that 
is an integral part of the screen. 

Screen » — The normal screening medium is 
either punched steel plate or woven wire 
cloth. Some screens are furnished with 



steel side wings. High noise levels are 
generated by the impact of the product on 
both the deck and wing liners. 

Screen discharge, — Typically, the over- 
size product from the top screen deck 
drops onto a steel discharge lip or di- 
rectly from the screen onto a steel plate 
in the crusher. The undersize product 
passes through the screening media and 
impacts a discharge chute, transfer con- 
veyor, or another screen deck. 

Crusher feed hopper or chute, — The feed 
to the crusher impacts a cylindrical- 
conical collection hopper that directs 
the feed into the crushing cavity. Often 
the feed to the crusher is sparse and the 
impacting product strikes the hopper in- 
dividually. A heavily fed (choke-fed) 
crusher has the opportunity for a bed of 
material to build up and, therefore, 
attenuate the noise. 

Crusher feed plate, — Most cone crushers 
are supplied with an abrasion-resistant 
metal feed plate. Product dropping into 
the crusher strikes the feed plate — par- 
ticularly if the crusher is not choke 
fed. 

Crusher feed cone, — Typically, the feed 
cone is lined with manganese steel plate 
for wear. The product fed to the crusher 
strikes the feed cone. 

Crusher main frame, — The shell sur- 
rounding the crushing cavity typically is 
impacted by product discharging from in- 
side the crusher. The shell acts as a 
radiator for all of the noise generated 
in the product reduction process from 
within the crusher itself. 

Crusher discharge, — The product dis- 
charged from the crusher is typically 
transferred via another steel chute to a 
belt conveyor that transports it to the 
next comminution stage or to a stockpile. 

These sources are common to all crush- 
ing and screening plants and are acces- 
sible without major disassembly of the 
plant . 



NOISE CONTROL TREATMENTS 

The noise associated with each of the 
sources is usually generated by the im- 
pact of the product on the steel compo- 
nents. The impact forces cause the com- 
ponents to resonate, creating airborne 
noise. 

Noise control treatments can be applied 
to — 

• Minimize the impact forces. 

• Damp a vibrating steel component. 

• Enclose the source to block the air- 
borne noise. 



the main frame. Noise measurements at 
plant operating positions and cleanup 
areas showed noise reductions of 4 to 7 
dBA. These reductions, which approxi- 
mately double the allowable exposure 
times in these work areas, should reduce 
the full-shift noise exposures of cleanup 
and maintenance personnel to within those 
specified by Federal regulations. 

At the primary crushing plant, an op- 
erating booth was manufactured and in- 
stalled to enclose the crusher operator. 
Noise measurements showed a reduction of 
approximately 20 dBA resulting in noise 
levels in the booth of less than 80 dBA. 

NOISE CONTROL TREATMENT COSTS 



• Enclose the worker to block the air- 
borne noise. 

At the two secondary plants addressed 
during the Bureau program, resilient ma- 
terials were applied at certain locations 
to minimize the noise produced by product 
impact on the structure. Specific treat- 
ments included — 



The costs, in 1981 dollars, for the 
treatments described for the two second- 
ary plants averaged $15,500 ($14,003 and 
$17,085) for materials. Quarry labor re- 
quired for installation of the treatments 
averaged 67.5 work-hours (66 and 69 h). 
The booth, purchased commercially, cost 
$4,919 (1981) and required 40 work-hours 
for installation. 



• Resilient impact pads installed on 
the wall and bottom of the screen feed 
chute. 

• Resilient liner for the screen feed- 
box. 

• Resilient screen decking. 

• Resilient liners for the screen side 
wings , 

• Resilient screen discharge lip. « 

• Resilient liner for the crusher feed 
hopper. 

• Resilient liner for the crusher feed 
cone. 

• Resilient crusher feed plate(s). 

In addition, an acoustical curtain was 
used to enclose the crusher shell to 
block the airborne noise radiating from 



These costs are for purchasing and in- 
stalling materials manufactured specif- 
ically for the three plants treated in 
this program. They are a good estimate 
for the costs of treating similar-sized 
plants using commercially available mate- 
rial and plant labor for installation. 
Costs will probably be higher for larger- 
sized plants, or for treatments Installed 
by an outside firm. 

MANUAL ORGANIZATION AND CONTENT 

This manual is primarily intended as a 
general guide for the design, selection, 
and installation of noise control treat- 
ments for crushing and screening plants. 
Most of the treatments discussed have 
been installed in two secondary crushing 
and screening plants, and the drawings 
and photos are oriented toward that type 
of plant. The treatments, however, are 
applicable to other plant sizes and 
types. 



The main portion of this manual divides 
the plant into major components for dis- 
cussion. The discussion for each compo- 
nent covers — 

• How the noise is produced. 

• Typical noise levels generated. 

• The design and selection of noise 
control treatments. 

• How the noise control treatments are 
installed. 

• Any potential problems created by 
the treatments. 

The manual also includes a section on 
the design, fabrication, and installation 
of control booths for protecting the 
plant operators. 



The manual is not plant specific. It 
does not specify materials by type, and 
does not specify dimensions. There are 
a number of well-known manufacturers of 
the types of materials recommended in 
this manual. It is not the Bureau's 
intent to make specific recommendations; 
the appropriate noise control treatment 
will depend on the actual operating 
conditions encountered and the noise 
levels measured at a plant. Thus, it is 
not possible to state exact dimensions or 
specific material requirements. The 
manual, however, does provide general 
design considerations, and does discuss 
what information must be provided by the 
plant operator to a noise-control 
material manufacturer to ensure proper 
material design. 



NOISE CONTROL TREATMENT OF THE SCREEN FEED CHUTE 



Typically, screens receive product to 
be processed via a steel chute that is 
fed by a belt conveyor. Product dis- 
charged from the conveyor strikes the 
sides and wall of the chute, rebounds, 
and falls to the chute bottom where it 
discharges to the screen through the 
feedbox (fig. 1). Noise levels measured 
adjacent to these chutes normally exceed 
110 dBA with a coarse product feed. 
Noise levels at normal operating posi- 
tions near these chutes approach 100 dBA. 



The recommended 
ments include — 



noise control treat- 



• Installing a resilient impact pad on 
the chute wall and/or sides. 

• Using a resilient impact pad or a 
product dead bed in the chute bottom. 

The purpose of these treatments is to ab- 
sorb the force of the product impact, 
thus reducing the amount of energy trans- 
ferred to the steel chute. If properly 



designed and installed, they will not on- 
ly reduce noise, but also significantly 
increase chute life. 



Belt conveyor 



Screen 
feed - 
chute 
wall 



Dribble chute 




Screen 
feedbox 

FIGURE 1, - Product feed path from the belt con- 
veyor to the screen feed box. 



DESIGN AND SELECTION OF 
RESILIENT IMPACT PADS 

Proper design of impact pads for maxi- 
mum noise reduction and minimum wear re- 
quires designing for — 

• Product type. 

• Product size. 

• Product impact angle. 

• Product velocity. 

The angle that the product strikes an 
impact pad will determine the life of the 
pad (see figure 2). Impact angles of 
less than 50° will result in rapid wear 
and less life than steel. Impact angles 
between 50° and 70° will yield a wear 
life comparable to steel. Angles greater 
than 70° and less than 90° are considered 
optimum. If the impact angle is 70° or 
above, the impact pad can be a flat 
sheet. If the angle is less than 70°, a 
profiled surface that provides a greater 
impact angle is recommended (fig. 3). 



Product Impact angle 
path N^ ^^ 



Impact angle 




Resilient pad 

FIGURE 2, - Effect of impact angle of product on 
resi lient pad life. 



u 



7, 



Product^ Impact angle 
path 




Poor design with o shotlow 
impact angle 



Good design using a profiled 
surface to increase the impact 
angle to greater than 70° 



FIGURE 3» • Use of a profiled impact pad to pro- 
vide a better impact angle for increased wear life. 

The thickness of the pad must be suffi- 
cient to minimize crushing damage to the 
liner. The required thickness depends 
upon both the size of the product strik- 
ing the pad and the velocity of the prod- 
uct at impact. Generally, the larger the 
product and the higher the velocity, the 
greater the thickness of material that 
is required for optimum wear. This in- 
creased thickness, however, must be bal- 
anced against available space within the 
chute. In small chutes, the rubber 
thickness could interfere with the head 
pulley or belt scraper and could retard 
product flow out of the chute. 

The type and the mechanical properties 
of resilient materials (selected for the 
impact pads) are site specific, and de- 
pend primarily upon the size, shape, and 
type of product being processed. 

Selection of the material, in terms of 
its hardness, thickness, and proper sur- 
face profile, should be the responsibil- 
ity of the material manufacturer. The 
user, however, must provide the follow- 
ing information for proper impact pad 
selection: 

Type of product being processed. 

Size of product being processed. 

Velocity of the product — for the chute 
side wall, the belt speed should be ade- 
quate; for the chute bottom, the height 
of the drop is required. 

Dimensions of the chute. 

Angle of product impact . 

Relative position of the head pulley, 
belt cleaner, and dribble chute. 



Representatives of companies of any 
potentially applicable resilient materi- 
als will definitely have to visit the 
quarry operations before specifying any 
products. This may be the only oppor- 
tunity for the material manufacturer 
and the quarry operator to actively dis- 
cuss the implied and explicit warranties 
of the resilient materials, the extent 
of the required labor needed for materi- 
al installation, and whose responsibil- 
ity it will be to make field modifica- 
tions to any improperly fitting resilient 
products. 

INSTALLATION OF THE CHUTE 
WALL IMPACT PAD 

The impact pad for the chute wall can 
be either bolted to the wall or suspended 
in the chute. Figure 4 shows a profiled 
surface pad installation. Holes are 
drilled or burned through the chute wall. 
Corresponding holes are drilled through 
the impact pad. Drilled steel bars 
should be placed between the resilient 
pad and boltheads for better support. 
The pad should be the full width of the 
chute wall and should extend both above 
and below the impact area. 

The pad can also be suspended in the 
chute using cables or steel straps that 
secure it to the chute side walls. If 




space permits , the pad can be suspended 
away from the chute wall, allowing it to 
swing freely. This will help reduce 
crushing forces on the pad and should in- 
crease its life. Care must be taken, 
however, to insure that the pad does not 
swing into the conveyor belt head pulley 
when the feed is shut down and the prod- 
uct flow into the pad stops. 

Once the pad is installed, the clear- 
ance between it and the head pulley 
should be checked regularly to ensure 
that the pad does not interfere with the 
pulley or belt scrapers. Additionally, 
the flow of the product in the chute 
should be observed. Using a resilient 
impact pad can change the angle at which 
the material rebounds from the chute wall 
(shown in figure 5). Depending on the 
chute depth, a change in angle might cre- 
ate another impact point before the prod- 
uct reaches the chute bottom; this may 
then require an impact pad for the drib- 
ble chute. An important caution is that 
the installation of impact pads may cre- 
ate material handling and/or equipment 
problems if the conveyor speeds are too 
high, if incorrect idlers are used, or if 
insufficient clearances exist around the 
conveyor. Specifications from the Con- 
veyor Equipment Manufacturer's Associa- 
tion for the design and installation of 
conveyors must be followed. Questions 
concerning proper design and fine tuning 
a conveyor system are best answered by 
the manufacturer. If dust control sprays 
are used in the chute, then adequate 
clearance has to be provided before in- 
stalling the impact pad. The water 



STEEL CHUTE 



Feed chute 




IMPACT PAD INSTALLED 



v,^^ Conveyor 



-^Dribble chute Feed chute 



Feedbox 




-^ Dribble chute 



Feedbox 



FIGURE 4» • Installation of a profiled-surface 
impact padt 



FIGURE 5. - installation of a resilient impact pad 
may cause a change in product rebound* 



sprays will have to be readjusted after 
restarting the circuit to accommodate any 
change in the rebound of the product. 

INSTALLATION OF AN IMPACT PAD 
OR DEAD BED IN THE CHUTE BOTTOM 

An impact pad should also be bolted to 
the bottom of the feed chute, as shown in 
figure 6. Holes can be drilled or burned 
through the chute after marking it to 
correspond to those that are drilled 
through the pad(s). The holes in the pad 
should be countersunk by the material 
manufacturer so the boltheads will be be- 
low the pad surface, as shown in fig- 
ure 7. The pad should cover the entire 
chute bottom. 

Most resilient materials have a higher 
coefficient of sliding friction than 
steel. Installation of the pad, there- 
fore, may tend to retard the product flow 
out of the chute. If product flow is un- 
satisfactory, the angle of the chute bot- 
tom may have to be increased to overcome 
the increased friction of the pad. 

The chute bottom can also be modified 
by creating a dead bed. A dead bed is 
nothing more than a buildup of product 
at the area of impact, A dead bed is 
created by installing a dam at the dis- 
charge end of the chute bottom (as shown 
in figure 8) to retard the product flow. 
The dam can be made from resilient mate- 
rial or channel iron, should be bolted to 
the chute bottom, and should extend the 
entire width of the chute. The height of 
the dam will depend on the angle of re- 
pose of the product flowing through the 
chute and the angle of the chute bottom.. 
It must be high enough to create a layer 
of product that covers the entire chute 
bottom. A dead bed is also recommended 



in combination with a resilient impact 
pad to improve the life of the pad. A 
combination of an impact pad and dead bed 
installed in a chute bottom is shown in 
figure 9; the impact pad is covered by 
the dead bed, however, and is not visible 
in the figure. 




FIGURE 6. - Installation of a resilient impact pad 
on the bottom of the screen feed chute. 




mpact pad 



7777 Chute bottom 



FIGURE 7, - Impact pad fastened to the bottom of 
feed chute with countersunk holes for protection of 
boltheads. 




Dam 




FIGURE 8. - Installation of a dam to create a dead 
bed on the chute bottom. 



FIGURE 9, - Combination of a resilient impact pad 
and dead bed in the bottom of a secondary screen feed 
chute. 



NOISE CONTROL TREATMENT OF SCREENS 



Typically, the product discharged from 
the screen feed chute impacts a steel 
feedbox that is an integral part of the 
screen. The product then passes over the 
screening medium, which is either punched 
steel plate or woven wire cloth. Depend- 
ing on the discharge trajectory, the 
oversize product either passes over or 
falls onto a steel discharge lip. Most 
screens are furnished with either steel 
side wings or with steel side-tension 
rails that are also impacted as the prod- 
uct passes along the deck. 

High noise levels are generated by the 
product impacting on the steel feedbox, 
on the deck, against the side wings or 
tension rails, and on the steel dis- 
charge lip. Noise levels measured beside 
screens handling coarse material often 
exceed 105 dBA. 

The recommended noise control treat- 
ments include — 

• Resilient linings for the screen 
feedbox. 

• Resilient screen decking. 



• Resilient side wing liners, or re- 
silient material liners on the side- 
tension rails, 

• Resilient screen discharge lip, 

DESIGN AND SELECTION OF NOISE CONTROL 
TREATMENTS FOR SCREENS 

Most screen manufacturers do not recom- 
mend discharging product directly onto 
the perforated part of the screen deck. 
This is especially true for screens hand- 
ling coarse product with a large drop 
height from the feed chute. These 
screens are provided with a blank metal 
panel at the feed end preceded by a feed- 
box that is often protected by metal wear 
plates where the product impacts the 
screen. The blank panel should be re- 
placed by a thicker, blank resilient pan- 
el. A resilient impact pad should be in- 
stalled in the screen feedbox to increase 
the thickness of the area that is im- 
pacted by the product from the feed 
chute. The back and sides of the screen 
feedbox should also be treated with a re- 
silient liner. 



10 



The screening medium (punched plate or 
woven wire) should be replaced with a re- 
silient deck. ;^n selecting the resilient 
deck, it must be remembered that the use 
of a resilient cloth may reduce screening 
efficiency and throughput. This reduc- 
tion can be caused by — 

• Less percent open area for the same 
deck area. 

• The resilient cloth (being thicker 
to maintain strength) may cause blinding 
of the screening medium, thus further re- 
ducing the percent open area in the deck, 

• Screening is normally accomplished 
in the initial one-third of the deck; if 
a screen is marginally sized for a spe- 
cific capacity, then arbitrarily replac- 
ing a perforated panel with a blank 
one will also reduce the screening 
efficiency. 

The actual thickness of the cloth de- 
pends upon the maximum feed size and the 
thickness of the bed depth. The cloth, 
however, should not be thicker than the 
size of the openings in the deck. 

When ordering resilient decking, it is 
important to specify the following infor- 
mation to the deck manufacturer: 

Use of the screen in the circuit (siz- 
ing, scalping, transferring, etc.). 

The efficiency of the screen (i.e., the 
percent near size and undersize material 
contained in the oversize product). 

Type and size of product being 
screened. * 

Dimensions of the existing deck. 

Type of mounting — whether the deck is 
bolted to the screen frame or if it is 
held by side-tension rails. 

Type, location, and dimensions of 
screen support members. 

Type and dimensions of holddown 
clamping. 



Resilient materiale are extremely dif- 
ficult to "modify-to-fit" in the field; 
thus, exact equipment dimensions must 
be provided to the resilient material 
supplier . 

If the deck is bolted to the screen 
frame, nonperf orated areas should be spe- 
cified over the deck support members. 
The nonperforated areas will protect the 
support members and prevent accumulation 
of product between the deck and supports , 
which can cause excessive wear of the 
frame. If the screen has steel side 
wings, resilient liners that are at least 
1 in thick and high enough to protect the 
side wings from product impact should be 
specified. 

If the screen cloth is attached using 
side-tension rails, the type and size of 
rail have to be specified. Most manufac- 
turers of resilient decks supply side- 
tension rails equipped with a resilient 
impact liner that is bonded or bolted to 
the rails. Trowel- or paint -on resil- 
ient coatings have had limited durabil- 
ity, and their use is not recommended. 

As mentioned, the type and size of sup- 
port members have to be specified. Sup- 
port members require a resilient protec- 
tive molding (shown in figure 10^4), 
called a bumper strip, to minimize deck 
wear and properly crown the deck. The 
type of deck clamping also has to be spe- 
cified. If the screen uses a center 
clamping bar, a resilient molding for the 
bar (fig, lOB) is available from the man- 
ufacturers. Screen clamping with J-hooks 
should use a resilient block or ring 
(fig, IOC) to protect the nut and threads 
on each hook. These blocks or rings are 
also available from the deck manufactur- 
er. The Bureau recommends ordering extra 
clamping hardware at the outset because 
any discontinuity on the screen deck sur- 
face appears to accelerate the wear on 
the clamping device. 

The discharge lip and sides should also 
be lined with resilient material. For a 
straight lip discharge, the thickness of 
the bottom pad should be the same as the 
thickness of the deck. The resilient 



11 



B 





FIGURE 10. - Cross section of typical 
resilient protection for sizing screens. 
A, Molding (bumper strip) for support mem- 
bers; B, molding for a center bar clamp; 
C, block or ring for a J-hook clamp. 

liners for the sides of the lip should be 
thicker than those on the side wings. 
Increasing the thickness of the side lip 
liner will funnel the screen discharge 
and help prevent product from being 
jammed between the screen and the screen 
discharge hopper, A horizontal screen 
discharge, which feeds a crusher directly 
by choking the feed down to the opening 
size of the crusher feed hopper, requires 
a resilient liner on both the sides and 
bottom of the discharge chute. To mini- 
mize installation problems, the exact 
size and shape of the chute bottom and 
sides should be specified. Most resil- 
ient liners that are used in coarse 
screening are reinforced with steel plate 
or woven wire; thus, modifying them in 
the field during installation is extreme- 
ly difficult and time consuming. 



INSTALLATION OF NOISE CONTROL 
TREATMENTS FOR SCREENS 

Treating the screen feedbox with a re- 
silient liner, installing an impact pad 
or plate, and replacing the perforated 
metal (or woven wire) deck with resilient 
decking is fairly straightforward, pro- 
vided the measurements were obtained 
carefully. Installation of a resilient 
deck that is to be bolted in place (fig. 
11) requires — 

• Removing the steel screen deck and 
blank feedbox panel. 

• Carefully measuring and locating 
bolthole locations on the resilient deck 
and blank feedbox panel (if not furnished 
predrilled) . 

• Drilling and countersinking holes in 
the resilient deck and feedbox panel (if 
not furnished predrilled). 



• Installing new 
required) . 



bumper bars (where 



• Bolting the panels in place. 

Figure 12 shows an inclined sizing 
screen equipped with a blank, resilient 
feedbox panel and a resilient screen 
deck. As mentioned earlier, a feedbox 
handling coarse material with a large 
drop height from the feed chute should 
have a thicker resilient pad at the point 
of impact. This pad can be bolted to the 
metal (screen) feedbox, as shown at the 
right of figure 13. 

Installation of the side wing liners, 
shown in figure 13, requires the follow- 
ing modifications to the previously in- 
stalled side wings: 

Drilling or burning boltholes through 
the top and bottom of the side wings. 
(CAUTION. — Do not drill through the side 
plates of the screen unless the manufac- 
turer has provided approval for the 
holes , since this can affect the struc- 
tural integrity of the screen.) 



12 



! 

® 



f 

® 



f 



rs> 



Up o o 



© 

o 



tk ♦ 






o o o o 



do o^ 

4 • 



10 o » 



o « 



a 



JMM^ 



SBtttt 






I 



r 



—J^ 



o| e o o o J© 

o I e e e e le 



FIGURE lit" Installation of a bolted resilient 
screen deck and blank impact panel* 




FIGURE 12, • Bolted resilient deck with blank 
panel in the feedbox. 




FIGURE 13, - Resilient feedbox with impact pad 
where product from the chute strikes the feedbox. 

Locating, drilling, and countersinking 
bolt holes through the resilient 
liner. 

Bolting the liner in place. 

Thicker liner sections (fig. 14) can also 
be bolted along the length of the side 
wings and/or at the discharge lip to fun- 
nel the product flow towards the center 
of the screen deck. An installed side 
wing liner is shown in figure 15. 

Installation of a resilient deck using 
side-tension rails is shown in figure 16. 
Installation requires — 

• Removing the steel deck and side- 
tension rails. 

• Locating, drilling, and countersink- 
ing boltholes through the resiliently 
lined, side-tension rails. 



13 



Side liners 



Thicker liner 







Discharge end 
FIGURE 14. - Installation of resilient side wing 



iners. 



Side wing 



,**■; 



/ * 



n^ 



Resilient liner 



\. 



'. ? 



^ ¥.-.- if .^ 




^.^1iC. 




i 



FIGURE 15. - Resilient liners bolted to screen 
side wings. 

• Installing resilient protective 
moldings (bumper strips) on screen sup- 
port members. 

• Installing the deck and side-tension 
rails on the screen frame. 

• Clamping the screen deck using 
either J-hooks with resilient protective 
blocks or rings, or using a center bar 
clamp with resilient protective molding. 

Figure 17 shows a resilient screen deck 
equipped with resiliently lined, side- 
tension rails that had been installed 
on a horizontal screen. The completed 




Resilient rings 



Side-tension rail 



iDDfjninQodu gaa quo \ 

/ooocoaaoaSaaaaa ^ 

/ccooaQaoomaaaaa < 

/coooooauuinau QQQ ' 

' DDUDoa DUD aaa aaa ' 

' DDDDDDDaUUUU aOQ ' 




Bumper strip 



'L J 



FIGURE 16. " Installation of a resilient screen 
deck using side-tension rails (longitudinal screen 
deck support). 




FIGURE 17. - Resilient screen deck with re- 
siliently lined, side-tension rails. 

installation with protected J-hook clamp- 
ing is shown in figure 18. 



14 




Side lip iiners 



FIGURE 18. • Resilient deck installed on a hori- 
zontal screen using resiliently lined, side«tension 
rails and J-hook clamps. 



Resilient liner for 
discharge lip 







^ 






¥ 



«-- JI/ o o\ o o ° ° 



w\ 



Discharge 
hopper 



FIGURE 19t • Treatment of the screen discharge lip. 



The screen discharge lip and discharge 
chute liners are also bolted in place. 
For the screen discharge lip (fig. 19), 
any existing steel wear plates are re- 
moved and the resilient liner is bolted 
in place. Side lip liners can also be 
bolted to the screen side wings. As men- 
tioned, the side liners installed at the 
discharge should be thicker than the side 
wing liners along the deck to funnel the 
material flow and prevent product from 
jamming between the screen and the adja- 
cent screen discharge hopper. Figure 20 
shows a resilient discharge lip and 
thicker side liners installed on an in- 
clined sizing screen. 

Installation of resilient liners for a 
screen discharge chute, which feeds a 
crusher by choking the product flow down 
to the size of the opening of the crush- 
er, is illustrated in figure 21. These 
liners are also bolted to the bottom and 
sides of the steel chute. Figure 22 
shows the treatment of a screen discharge 
chute at a secondary sizing plant. Note 
that the boltheads are countersunk in the 
resilient material to protect against ex- 
cessive wear caused by product slid- 
ing over them, and also to eliminate a 




FIGURE 20. - Resilient discharge lip with thicker 
side liners to funnel the screen discharge. 

potential secondary noise source that is 
caused by the product striking the metal 
bolthead. 

The use of a resilient screen deck can 
cause potential operating problems, 
primarily decreased screening efficiency 
because of plugging of screen openings. 
These problems have already been 



15 




discussed earlier in this report, 
potential problems include — 



Other 



m 



^;m§^mm 




FIGURE 2], - Installation of resilfent liners on a 
screen discharge chute. 




FIGURE 22» = Resilient liner in a screen discharge 
chute directly feeding a crusher. 



• The product tends to bounce more on 
a resilient deck, especially on an in- 
clined screen receiving coarse product, 

• Resilient decks may require changes 
in the screen's throw amplitude, speed, 
and direction to maintain the usual 
productivity and screening efficiency. 
Most screens have this flexibility; if 
changes are required, the manufacturer or 
the screen operating manual should be 
consulted. 

When product strikes a resilient sur- 
face, it tends to bounce more than when 
it strikes steel. This higher bounce 
combined with the increased thickness of 
a resilient screen deck can result in 
clearance problems between the deck and 
either overhead or between-deck vibra- 
tors. If product does strike the vibra- 
tor, a resilient pad should be added to 
the vibrator housing to prevent potential 
damage. Another alternative for an over- 
head vibrator would be to install a 
spreader curtain at the screen feed end. 
This spreader curtain, made of used con- 
veyor belting, can be attached to the 
feed chute to help distribute the screen 
bed depth uniformly and minimize product 
bounce. The belting should be attached 
to the chute and extended to the under- 
side of the vibrator. Do not attach the 
belting to the vibrator; rather let it 
hang free to raise as product passes un- 
der it. 

The higher bounce can also create safe- 
ty and feed distribution problems , par- 
ticularly on an inclined screen process- 
ing coarse feed. The product striking 
the resilient impact pad in the screen 
feedbox may tend to bounce further down 
the screen, thus negatively affecting the 
distribution of the product along the 
screening surface; given the right set of 
circumstances, the product may bounce 
over the screen side wings. To eliminate 
both the feed distribution and safety 
problems , a drag curtain should be in- 
stalled over the feed chute discharge 
(fig. 23). 



16 







D O lO O 



1 



O O O I., 
© O © Q\ 

Q O O d' 



>Z!C> lO O O Q O <t) 1 



'm 



FIGURE 23, - Installation of a drag curtain 
over the feed chute discharge. 



The drag curtain should be made of a 
heavy, abrasion-resistant, resilient ma- 
terial. (Conveyor belting is not recom- 
mended because it wears rapidly and does 
not have enough mass to retard the prod- 
uct flow.) The drag curtain should be 
the full width of the screen and should 
extend from the top of the feed chute 
discharge opening to the end of the blank 
panel. The curtain can be bolted to the 
feed chute; installation of a drilled 
steel bar, inserted between the curtain 
and the boltheads , is recommended for 
added support. A drag curtain that has 
been installed on an inclined sizing 
screen is shown in figure 24. 

The use of a resilient deck may also 
require changes in the screen's throw am- 
plitude, speed, and direction to maintain 
productivity and screening efficiency. 
For example, if the screening efficiency 
decreases (too much near-size product is 
being discharged off the screen deck) , 
the throw direction can be changed from 
with-flow to counterflow rotation. If 
the bed depth becomes too shallow, the 
speed can be reduced along with the throw 
direction. This will result in a thicker 
bed depth. The amplitude of the throw 
can also be varied to obtain a more de- 
sirable operating condition. In fact, 
all three of these parameters may have to 
be changed to optimize the screening 
capacity and efficiency. 




FIGURE 24, • Drag curtain installed on an inclined 
screen. 



17 



Although these changes were not made at 
any of the three cooperating quarries, 
the researchers had discussed these pos- 
sibilities with them. An important point 



to remember is that manufacturer's recom- 
mendations should always be requested 
before any operating parameters are 
changed . 



NOISE CONTROL TREATMENTS FOR A CONE CRUSHER 



A typical secondary crushing and 
screening plant uses a cone crusher to 
reduce the oversized product from the 
screen. This oversized product is trans- 
ferred into a steel hopper that feeds the 
crusher and then into the crusher feed 
cone, which is typically equipped with 
steel wear liners. The screen discharge 
also strikes the crusher feed plate 
and/or the mantle hold-down cap. 

High noise levels are generated when 
the product impacts these steel compo- 
nents , and by the actual crushing pro- 
cess , which produces noise from the 
crusher main frame. Noise levels mea- 
sured beside cone crushers typically ex- 
ceed 110 dBA. 

The recommended noise control treat- 
ments for a cone crusher include — 

• Resilient liners for a surge-type 
feed hopper, feed cone hopper shell, and 
the feed cone. 

• A resilient feed plate or pad for 
the mantle hold-down cap. 

• A barrier curtain around the exte- 
rior of the crusher main frame, 

DESIGN AND SELECTION OF NOISE CONTROL 
TREATMENTS FOR CONE CRUSHERS 

Noise treatments for the crusher surge 
hopper, feed shell, and cone should be 
designed after the resilient deck has 
been installed and any adjustments to the 
screen have been completed. This se- 
quence of treatment is recommended be- 
cause the product flow from the screen 
may change, thus changing the impact 
points in the feed hopper. The crusher 
feed cone and the feed cone hopper can be 
treated completely because they rotate 
during liner wear and/or setting. Re- 
silient linings are required for all hop- 
per surfaces impacted by the product. 



not only during full-load operation, but 
also during screen startup and shut- 
down. Proper design of the liner for 
the crusher surge hopper requires sup- 
plying the manufacturer the following 
information: 

Size and type of product. 

Drop height or velocity of the product 
at Impact. 

Dimensions of the hopper. 

Sketch of the hopper showing impact 
areas. 



Location of 
bars, if used. 



dust suppression spray 



the lining may 
in sections to 
handling pr ob- 
is recommended 
be interchange- 



If the hopper is large, 
have to be manufactured 
minimize installation and 
lems. Additionally, it 
that the lining sections 
able, if possible. This flexibility will 
allow the panels to be rotated to accom- 
modate uneven wear rates. It is also 
recommended that the lining be designed 
so that it can be suspended away from the 
hopper wall. This type of installation 
will reduce the localized crushing forces 
on the liner, and thus reduce the re- 
quired liner thickness. 

Resilient linings are also recommended 
for the crusher feed shell and cone. 
Care has to be taken in sizing the liner 
thickness so the thickest liner possible 
can be used, and yet not interfere with 
the material flow through the crusher. 
Ideally the shell and cone liners should 
be a one-piece assembly. This one-piece 
assembly can be simply inserted over the 
existing shell and cone or replace the 
fabricated steel liner assembly. The 
lining can also be manufactured as seg- 
ments for easier handling and attaching 
to the existing steel liners. This is 



18 



not recommended, however, because of the 
possibility of a segment coming loose and 
passing through the crusher, which can 
cause significant damage. Another bene- 
fit of the full assembly, particularly on 
crushers without a rotating bowl, is that 
the liner can be rotated for more even 
wear. 



along the top edge of the curtain to pro- 
vide easy installation on bolts that can 
be welded to the adjustment ring. The 
curtain should be long enough to go com- 
pletely around the crusher, plus one 
extra foot for an overlap that will 
ensure the acoustical Integrity of the 
treatment. 



For cone crushers with a steel feed 
plate, the plate should be replaced by 
one manufactured with resilient material. 
The new feed plate should be cast by the 
material manufacturer using a mold that 
matches the steel one. It is, however, 
recommended that the resilient plate be 
manufactured thicker and larger in diam- 
eter than the steel one to prevent pre- 
mature failure of the material located 
between the hold-down bolts and the out- 
side diameter of the plate. Additional- 
ly, the resilient feed plate should be 
manufactured with an integral steel cen- 
tering plate to match the machined female 
fit of the feed distributor or the main 
shaft nut. Replacing the steel plate 
with a resilient one will not affect the 
unbalanced forces of the crusher. 

For crushers without a feed plate, a 
resilient pad for the mantle hold-down 
cap is recommended. The pad would also 
have to be custom cast by the material 
manufacturer to match the existing hold- 
down cap. This treatment is not neces- 
sary if the crusher is consistently choke 
fed. A crusher that is choke fed has 
sufficient product in the crushing cavity 
to protect the mantle hold-down cap from 
impact. This is the same noise control 
technique as the dead bed for a product- 
transfer chute. 

To control the noise radiating from the 
crushing zone and from product impacting 
the main frame liner, an acoustical bar- 
rier curtain should be installed around 
the crusher exterior. The curtain should 
be fabricated from loaded vinyl that has 
a layer of absorptive material on one 
side. The material should be purchased 
wide enough to extend from the adjustment 
ring to the base of the main frame 
flange. Grommets should be specified 



INSTALLATION OF NOISE CONTROL 
TREATMENTS FOR CRUSHERS 

The resilient liner for the crusher 
feed hopper can be either bolted directly 
to the hopper wall or can be suspended 
away from the wall to improve wear. A 
suspended liner is shown in figure 25. 
In this suspended installation, the liner 
was bolted to the hopper wall along the 
top edge and allowed to hang freely. The 
bolts, which are above the impact area, 
did not have be be countersunk in the 
material. 

The crusher feed cone shell and feed 
cone liners, if fabricated as a one-piece 
assembly, can be simply forced into place 
(fig. 26). This is done after removal of 
the steel wear plates or bars that might 
have been installed. The shell liner can 
also be bolted in place with a steel ring 
for added support. An installed one- 
piece resilient crusher feed cone is 
shown in figure 27. 




FIGURE 25. • Resilient liner installed in the 
crusher feed hopper. 



19 




FIGURE 26. - Installation of a resilient crusher 
feed cone shell liner* 

The installation of a segmented resil- 
ient feed cone liner requires — 

• Removing any steel wear liners. 




FIGURE 27* - Installation of a one-piece resilient 
crusher feed cone liner. 



• Locating, drilling, and countersink- 
ing boltholes in the resilient liner seg- 
ments (if not ordered that way from the 
material vendor), 

• Bolting the segments in place. 

The installation of resilient liner 
segments in a feed cone is shown in 
figure 28. 

The installation of the resilient feed 
plate (fig. 29) is straightforward. The 
old feed plate is removed and the new 
feed plate is bolted in place. 

Installation of a resilient pad on the 
mantle hold-down cap (fig. 30) would 
require — 

• Cleaning product from the recess for 
the main shaft bolt. 

• Welding a mounting bolt for the pad 
on the head of the main shaft bolt. 

• Installing the pad, making sure that 
the bolt and nut are below the pad 
surface. 



• Burning or drilling boltholes 
through the feed cone. 



20 




FIGURE 28. - Installation of resilient feed cone 
liner segmentst 




FIGURE 29» - Installation of a resilient crusher 
feed plate* 

The noise barrier curtain (fig. 31) is 
attached to the adjustment ring and hangs 
freely to the base of the main frame 
flange. This free hanging will allow 
vertical movement when the crusher passes 



Fillet weld to 
feed cone 




FIGURE 30, - Installation of a molded resilient pad 
for the mantle hold-down cap. 



tramp iron and will not interfere with 
normal crusher servicing. Installation 
of the curtain requires the following: 

• Use the curtain grommets as a tem- 
plate to mark locations on the crusher 
adjustment ring. 

• Weld studs or cap screws to the ad- 
justment ring at the marked locations, 

• Mount the curtain on the studs or 
screws. 

• Make cutouts in the curtain for hy- 
draulic lines and around the crusher 
countershaft box. 



An Installed curtain is 
figure 32. 



shown in 



21 



Fillet weld bolt to 
ajustment ring 

(Srl 




^ Cut out for countershaft, 
as needed 



^^Cut out for hydraulic 
lines, OS needed 




FIGURE 31. - Installation of a barrier curtain around 
the crusher main frame. 



FIGURE 32» - Noise barrier curtain installed around 
the crusher main frame. 



NOISE CONTROL USING AN OPERATOR CONTROL BOOTH 



The noise control treatments described 
in the previous sections were aimed at 
reducing noise at the source or enclosing 
the noise source. Another treatment, 
which is extremely cost effective for 
stationary plant employees, is the con- 
struction of a control booth, A control 
booth is not expensive to construct or 
purchase, can provide noise reductions of 
15 to 25 dBA, requires very little main- 
tenance after installation, and also 
helps protect the operator from the 
weather and other environmental hazards, 
such as dust. 

GENERAL SELECTION GUIDELINES 

The construction or purchase of a booth 
is straightforward and quite a number 
have been installed in the industry. 
Many, however, are not as effective as 
they could be for the following reasons: 

The booth is not large enough. 

The booth does not have adequate air- 
conditioning. 

The booth does not provide the operator 
an adequate field of view. 



The booth is not acoustically tight. 

The booth is mounted directly on the 
plant structure. 

For a control booth to be effective, it 
not only has to reduce the noise, but al- 
so has to provide enough comfort so the 
operator will stay inside the booth dur- 
ing normal plant operation. An operator 
will not stay in a booth if it is too 
cramped, too hot, or does not provide 
adequate visiblity. 

If a booth is going to provide maximum 
noise reduction it must be tightly con- 
structed. Any holes or openings in the 
booth will let outside noise pass inside. 
Many plants have installed booths that 
look nice, but do not provide adequate 
noise reduction because they fail to seal 
leaks (after construction) around doors, 
windows , or where control cables have to 
pass through the booth. These types of 
leaks can easily reduce the effectiveness 
of a booth by 10 to 15 dBA. 

The effectiveness of a booth can also 
be compromised by where and/or how it is 
mounted. A booth mounted directly on the 



22 



plant structure will have vibrations from 
this structure pass directly into the 
booth's structure. This vibration, which 
is usually severe, causes the booth's 
surfaces to radiate noise. If the booth 
has to be mounted on the plant structure, 
correctly designed vibration isolators 
will have to be used. An alternative 
would be to mount the booth on a separate 
structure that is not in contact with the 
plant; the plant controls would have to 
be relocated to the booth. 

GENERAL CONSTRUCTION GUIDELINES 

A control booth can either be purchased 
or can be constructed by plant labor. 
The construction of an effective booth, 
however, requires some modification of 
standard building practices. 

The walls of an effective booth can use 
a standard 2- by 4-in stud construction, 
with a 5/8-in plywood exterior. The in- 
terior, however, should have a double 
layer of gypsum wallboard with staggered 
joints. The wall should be insulated 
with a fiberglass that is attached to the 
exterior wall; this is primarily for tem- 
perature control. The thickness of the 
fiberglass should be less than the thick- 
ness of the stud. The basic construction 
is shown in figure 33. 



staggered joints) is recommended, 
tightly sealing the wall joints. 



as is 



The windows should be double pane with 
a 3/ 4-in air gap between them. The win- 
dows should be mounted in the frame using 
rubber gaskets to provide a tight seal. 
The windows should be large enough to 
provide the operator with an adequate 
field of view, but no larger. Windows, 
even double pane, are less effective 
noise barriers than the surrounding 
walls. Making the windows larger than 
necessary will reduce the effectiveness 
of the booth. 

The doors for the booth should be solid 
core. They can be either solid wood or a 
metal skin with an insulating foam core. 
The doorframe should also be gasketed to 
provide a tight seal. 

After the booth is constructed, check 
for and plug all leaks. As mentioned be- 
fore, this step is critically important 
and can increase the effectiveness of the 
booth by 10 to 15 dBA. Areas to check 
include — 

• Doorframes and window frames, 

• Wall-to-wall, wall-to-roof, and 
wall-to-floor joints. 



The roof of the booth can be a standard 
construction, but must be sealed at the 
wall joints. A drop ceiling using acous- 
tical tile is recommended inside. The 
booth floor can also be standard 
construction. A double floor layer (with 



X 4-in X 8-ft stud 



INSIDE 




OUTSIDE 



/s-in gypsum panel 



/e-ln plywood 
2-/4-10 fiberglass 



/2-in gypsum panel insulation (R II) 

FIGURE 33, - Basic control booth waif construction. 



• Holes cut for control and power 
lines. 



• Holes cut 
heater. 



for air-conditioner and 



It is also important to include the 
booth on a regular maintenance schedule. 
Gaskets and seals around doors and win- 
dows, for example, should be routinely 
checked and repaired. 

TYPICAL BOOTH INSTALLATION 

The control booth installed, during 
this research program, for a primary 
crusher operator is shown in figures 34 
through 37. The 8- by 10-ft booth was 
purchased for $4,919. 
mounted on a separate 
that was constructed by 
using 6-in I-beams. It reduced the noise 
levels at the operator's location from 97 
to 78 dBA. 



The booth was 

support structure 

quarry personnel 



23 




FIGURE 34. - View of a primary crushing plant with 
an operator control booth. 



FIGURE 35. • Operator control booth mounted on 
separate steel support structure. 




FIGURE 36. - Separate control booth support struc- 
ture constructed by quarry personnel. 



FIGURE 37. • Primary crusher operator at the con- 
trol station inside the booth. 



24 



SUMMARY AND CONCLUSIONS 



Treatment techniques employed the 
use of commercially available, wear- 
resistant, resilient materials. These 
products can be utilized for noise abate- 
ment by all sizes of crushing and screen- 
ing operations. Treatment costs for the 
portable plants were about 5 to 7 pet 
of the purchase price of a new 200- to 
300-ton/h plant. Reasonably maintained 
plants invest this amount annually to 
repair material handling equipment or 
product transfer points. The wear per- 
formance, the noise reduction, and the 
reasonable cost of the resilient products 
have led to the conclusion that retrofit 
noise treatments can be economically 
applied to all sizes of crushing and 
screening plants. Additionally, manufac- 
turers of crushing and screening plants 
can easily incorporate noise control 
technology as the plants are built, thus 



addressing additional noise sources. A 
retrofit program can only modify field- 
accessible areas; new plants, however, 
can be designed and fabricated to incor- 
porate resilient materials for improved 
wear and noise control from the beginning 
of the project. For example, the sizing 
screen feedbox seems to be a high mainte- 
nance area; the feedbox could be routine- 
ly fabricated with a resilient impact pad 
incorporated for the requirements of a 
specific plant. Cost tradeoffs for new 
plants are possible when wear-resistant, 
resilient materials are substituted for 
abrasion-resistant metals. Thus, the 
program results have indicated that the 
modifications that were tested could be 
expected to result in lower noise levels 
and reduced maintenance when applied to 
the design of a new plant. 



INT.-BU.OF MINES, PGH., PA. 27 51 1 



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